A certificate chain establishes trust by linking a server's certificate back to a trusted root certificate authority (CA). Here’s a step-by-step guide, incorporating the provided reference, on how to create one using multiple intermediate CAs:
Understanding Certificate Chains
A certificate chain, also called a chain of trust, is a hierarchical structure where each certificate is signed by the one above it in the hierarchy. This establishes an unbroken path from a server’s certificate to a trusted root certificate. This trust is essential for secure communications and verifying the authenticity of digital identities.
Creating a Certificate Chain: Step-by-Step
The following steps outline how to build a certificate chain, using multiple intermediate Certificate Authorities, referencing the provided document.
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Create a Root CA (Self-Signed):
- This is the top-most certificate in the chain.
- It acts as the foundation of trust.
- The root CA certificate is self-signed, meaning that it is signed by its own private key.
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Create an Intermediate CA1:
- This is a certificate that signs other certificates.
- It is subordinate to the Root CA.
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Sign Intermediate CA1 from Root CA:
- The Root CA signs the Intermediate CA1 certificate, establishing the first link in the chain.
- This creates a trust relationship.
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Create an Intermediate CA2:
- This is another intermediate certificate under the jurisdiction of Intermediate CA1.
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Sign Intermediate CA2 from Intermediate CA1:
- Intermediate CA1 now signs Intermediate CA2, establishing the next chain link.
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Create an Intermediate CA3:
- This is an intermediate certificate that is below Intermediate CA2 in the chain.
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Sign Intermediate CA3 from Intermediate CA2:
- The Intermediate CA2 signs the Intermediate CA3 certificate, further lengthening the chain.
Practical Considerations
- Intermediate CAs help protect the Root CA which is very sensitive, from exposure.
- Creating multiple Intermediate CAs can improve the organization and security of your public key infrastructure (PKI).
- You can create as many Intermediate CA's as required.
Example Visual of Certificate Chain
| Level | Type | Signed By |
|---|---|---|
| 1 | Root CA | Itself (Self-Signed) |
| 2 | Intermediate CA1 | Root CA |
| 3 | Intermediate CA2 | Intermediate CA1 |
| 4 | Intermediate CA3 | Intermediate CA2 |
| 5+ | Server Certificate | Intermediate CA3 or below |
How to Use
Once you've created your certificate chain, your server certificate should include all certificates in the chain, from the server certificate, up to but excluding the root certificate. Clients, who have the root certificate installed, will then be able to verify the server certificate using the full chain.
